2,3-epithiopropyl n,n-dialkylthiolcarbamates and use as herbicides



United States Patent 3,510,290 2,3-EPITHIOPROPYL N,N-DIALKYLTHIOLCAR- BAMATES AND USE AS HERBICIDES William Carter Doyle, Jr., Shawnee Mission, Kans., as-

signor to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Filed Mar. 24, 1967, Ser. No. 625,603

Int. Cl. A01n 9/12; C07d 59/00; C07c 155/02 US. Cl. 71-90 4 Claims ABSTRACT OF THE DISCLOSURE By a method of synthesis based on a secondary amine, carbon disulfide and epichlorohydrin there are produced 2,3-epithiopropyl N,N-dialkylthiolcarbamates which are used as selective herebicides, particularly in pre-emergent control of grasses such as brome and volunteer oats.

SUMMARY OF INVENTION It is known that reaction of carbon disulfide with a secondary amine readily produces the amine salt of a corresponding dithiocarbamate, as illustrated below:

The product obtained by this reaction is often employed in manufacturing dithiocarbamate salts and esters.

It has now been discovered, however, that by reaction of an N,N-disubstituted dithiocarbamic acid or its salts with epichlorohydrin, valuable herbicidal products are produced which are not dithiocarbamates but which apparently result from a combined esterification and intramolecular rearrangement. The course of the reaction is illustrated as follows:

(unstable) The product possesses very selective herbicidal activity against a few grasses, particularly brome and oats, and is readily converted to the corresponding epithio ester which possesses similar herbicidal activity and greater chemical stability:

The highly selective pre-emergent phytotoxicity of the novel compositions is particularly useful for application at the time of planting such crops as alfalfa and corn. Certain specific compounds of the group may also be applied at the time of planting soybeans and cotton. The preferred selective pre-emergent herbicides are 2,3-epithiopropyl N,N-dihydrocarbon substituted thiolcarbamates in which the two hydrocarbon substituents contain a total of 3,510,290 Patented May 5, 1970 less than ten carbon atoms. The hydrocarbon substituents may include alkyl, cycloalkyl from cyclopropyl to cyclohexyl and lower alkenyl groups.

methods, one a three-step process, with isolation of intermedlates and the other essentially a single-step process.

III II The initial low temperature reaction is believed to include reaction of epichlorohydrin with N,N-dialkyldithiocarbamic acid.

Method B R S O R (H) III The reaction of epichlorohydrin with a salt (which may also be a metal salt, as well as an amine salt) appearsto require a higher temperature than reaction with the acid.

In an experiment in which both routes were used to prepare the same N,N-diethyl thiocarbamate compound, the yields were roughly equivalent. In syntheses based on morpholine, dicyclohexylamine or isopropyl cyclohexylamine as starting materials, Method B has been found to be the only successful route, with the dithiocarbamate salt being the sole product obtained in the first step of Method A, rather than the more reactive free acid.

Intermediates I and II are isolable, though not easily purified. I is thermally unstable, rearranging to II in a matter of several hours to several days, depending on the nature of the N substituents. The structure of I is thought to be as shown, based on its infrared spectrum and the NMR spectrum of its phenylurethane derivative. Intermediate II is relatively stable and suitable for herbicidal use, various type II compounds showing qualitatively the same activity as the corresponding type III compounds. The structure of II is not firmly established but present evidence favors the stmcture shown in the reaction diagram below.

3 Newman- 011,

On treatment with acetyl chloride both II and IH give compounds (IV) having the same NMR spectrum and, while this spectrum is not readily interpreted, and a mixture of position isomers cannot be excluded, comparison with model compounds suggests the structure shown.

The success of this sequence of reactions leading to a thiolcarbamate apparently requires a secondary amine as starting material. In three instances in which a primary amine was used the crude products decomposed extensively and no epithiopropyl thiolcarbamate (III), was obtained. In one experiment, starting with tert.-butyl amine, tertvbutyl isothiocyanate was found among the products of decomposition.

The final products (III) of the sequence are distillable liquids or crystalline solids. Some care must be exercised to prevent excessive heating during distillation. Otherwise the following decomposition readily occurs:

This thermal decomposition, if desired, may be used as an efiicient and probably the most economical method of preparing allyl thiolcarbamates, which are products of established utility. (See, for example, British Patent 808,753.)

(II) Illustrative procedures Method A.-To a well-stirred mixture of 38.0 g. (0.5 mol) of carbon disulfide and 46.3 g. (0.5 mol) of epichlorohydrin in an ice-salt bath is added 36.5 g. (0.5 mol) of anhydrous diethylamine during 1-2 hours at to --5. The mixture is stirred an additional 30 minutes, then let wann slowly to room temperature. At this point the reaction mixture is essentially 3-chloro-2-hydroxypropyl N,N- diethyldithiocarbamate, (I; R, R'=Et), a viscous yellow oil with no detectable unreacted starting materials present.

Heating of the reaction mixture for 2 hours at 80-90 under vacuum gives 110 g. of crude rearrangement product II (R, R"=Et). The course of the rearrangement may be easily followed by the disappearance of infrared absorption bands at 2.95 2 (OH) and 10.15 1. (C=S) with the appearance of bands at 3.92 (SH) and 6.0g. (C=0). The rearrangement is also accompanied by a marked decrease in viscosity.

To 29 g. (0.12 mol of the crude rearranged product in 100 ml. of ether is added slowly 12 g. (0.12 mol) of triethylamine. Reaction is immediate, causing the ether to reflux gently and precipitating 10.8 g. of triethylamine hydrochloride. The solution is filtered, evaporated and vacuum distilled, giving 15.1 g. (61.4% yield overall) of 2,3-epithiopropyl N,N-diethylthiolcarbamate (III; R, R'=Et), b 119-20.

Method B.--A solution of 36 g. (0.173 mol) of diethylammonium diethyldithiocarbamate and 15.0 g. (0.162 mol) of epichlorohydrin in 100 ml. of dioxane is heated to reflux. Shortly after heating is begun, a crystalline precipitate appears. After two hours, the solution is cooled and filtered to recover 15.4 g. of diethylamine hydrochloride. The filtrate is vacuum distilled to remove the bulk of the solvent, leaving 33.2 g. of a viscous brown oil. Extraction of this oil with ether, decantation and evaporation of the ether gives 25.7 g. of residue, distillation of which gives 17.7 g. of III, R, R'=Et.

In Table I are listed the compounds of type III prepared by the above procedures.

4 TABLE I /NCSCH2CH-CH2 Percent Method Yield B.P. or M.P.

61. 4 l1920/0.2 mm. 1 53. 3 -20IL2 mm. 46. 5 133-4/1.2 mm.

Propyl Isopropyl Is0pr0pyl- A 54.0 117-18/0.4 mm. Hexyl Hexy A 52. 5 128-60l0 8 mm CH2CHzOCH2CHz B 1 34. 1 74-5". Methyl Methyl B 1 0.0 95107/0.3 mm. A] l Allyl A 35.0 12833/0.1 mm. 2-rnethoxy- 2-rnethoxy- A 24. 0 55/0.3-0.45 mm.

ethyl. yl. Butyl Butyl A 60.5 14353/0.5-0.9 mm. Isobutyl Isobutyl A 24.0 140-3/0.5 mm. Benzyl Methyl A 73.0 Crude material, not

distillable no 1.5974. Benzyl Isopropyl- A 77. 5 Crude material, not

distillable on 1.5773. Isoamyl Isoamyl....- A 23.0 15766/0.1-0.9 mm. Butyl Methyl A 49.5 13740/0.9 mm. Benzyl Benzyl A 72.5 Crude material, not;

distillable 11.13 1.6142. Furfuryl- Methyl A 86.0 Crude material, not;

distillable m5 1.5763. Tetrahydro- Methyl A 53. 5 Crude material, not;

furfuryl. distillable 1m 1.5581. Octyl Methyl A 88.5 Crude material, not

distillable no 1.5156. Cyclohexyl Methyl A 86.0 M.P. 55.558". Ethyl. 9. 5 1226/0.1 mm. Methyl 46. 0 129-34/0.8 mm. Ethyl" 56. 5 129-3l/0.8 mm. Isopropyl 1 90.0 Crude material, not

distillable m) 1.5500. Cyclohexyl--. CyclohexyL. B 1 88.0 M.P. 96.698. Cyclohexyl..- Ethyl A 82.0 Crude material, not distlglable m) 1.55

1 Yield based on epiehlorohydrin charged. 2 Crude product crystallized and was recrystallized from hexane.

(III) Herbicidal use Pre-emergent herbicidal activity was evaluated by means of the following procedure:

A solution was prepared by dissolving 290 mg. of the compound to be tested in 200 ml. of acetone. Disposable paper half-flats were prepared and seeded, then sprayed with the acetone solution at the rate of 20 pounds of active chemical per acre of sprayed area. One flat, which had been seeded with alfalfa, brome, flax, oats, radishes and sugar beets was held at 75 F. day temperature; another seeded with corn, coxcomb, cotton, crabgrass, millet and soybeans was held at 85 F. Twenty-one days after seeding and treatment the flats were examined and plant emergence and effects on growth were rated according to the schedule set forth below.

Type of action: I

C=chlorosis (bleaching) N=necrosis G=growth inhibition F=formative eflfect (abnormal form of growth) K=non-emergence Degree:

0=no effect 1=slight etfect 2=moderate effect 3=severe effect 4=maximurn effect (all plants died) Following are tabulated the results of tests according to the above procedures on a representative group of thiolcarbamates.

PRE-EMERGEN'I HERBICIDAL ACTIVITY Compound i N- SCH2CH----CH2 Orab- Cox- Soyugar R R grass comb Brome Millet beans Cotton Alfalfa Oats Corn Flax Radish Beet Ethyl Ethyl G1 F1 G Isopropyl Isopropyl G1 K4 G2 Propyl Propyl G3 G3 F3 G1 K4 F3 Hexyl. Hexyl 0 0 0 0 Butyl Ethyl G2 G2 F2 0 K4 F2 Isopropyl Ethyl 0 0 K4 0 Cyclohexyl Isopropy1 G1 K2 G1 F1 0 G2 F1 Cyclohexyl Ethyl G1 G1 F 0 K4 Fl Oyelohexy1 MethyL. 6..., Butyl Methyl 0 0 0 0 Methyl Methyl 0 0 0 0 Butyl Butyl K3 K3 K3 G3 G3 K4 G3 Isobutyl Isobutyl. K3 K3 G G1 K4 333 R 0 Cl g o 0 oFl g1 1 0 0 o 0 G2 G3 F2 G1 G1 0 F3 0 0 G1 0 o o 0 0 G2 0 o o 0 G2 G1 G3 F F2 0 0 F1 F3 0 0 0 G1 Cyc1ohexyl Ethyl K3 G1 K3 G3 G2 G3 G2 G2 G1 F1 G3 0 G2 G2 G2 Isobutyl Isobutyl K3 G1 G1 G1 G3 K4 01 0 G1 G2 0 0 0 G2 Butyl Butyl K2 K3 K2 G2 G3 G2 K4 0 G1 0 o 0 G2 Allyl Allyl K2 0 G2 G2 G1 G1 0 0 0 0 G2 The tabulated data indicate clearly the pronounced selectivity of the pre-emergent herbicidal action of the compositions. Also demonstrated in the data is an absence of activity toward the test species when the N-substituents contain a total of twelve carbon atoms. Although lacking in the desired type of herbicidal activity, the higher N,N-dialkylthio1carbamates are useful for other purposes, particularly in corrosion-inhibiting formulations, alone or in combination with nitrogen bases of the polyamine type, and as fungicides. The compounds derived from the higher molecular weight secondary amines in general exhibit microbiological activity without substantial effect on plant life.

What is claimed is:

1. The method of combating weeds which comprises applying to the locus of the weed seeds a herbicidally efiective amount of a compound represented by the structural formula R O S N' 1 )-SCH2Cfi -CH2 in which R and R represent hydrocarbon substituents containing a total of less than ten carbon atoms.

2,989,393 6/1961 Tiller et al. 71100 X JAMES O. THOMAS, JR., Primary Examiner US. Cl. X.R. 

